1. Field of the Invention
The present invention relates to a processing jig for holding an object processed with a processing apparatus.
2. Description of the Related Art
A floating thin film magnetic head used for a magnetic disk device and so on is generally made up of a slider and a magnetic head device provided at the trailing edge of the slider. The slider generally comprises a rail whose surface functions as a surface facing a medium (referred to as medium facing surface in the following description) or an air bearing surface and a tapered section or a step near the end on the air inflow side. The rail floats slightly above the surface of a recording medium such as a magnetic disk by means of air flow from the tapered section or step.
A thin film head device generally used is a composite-type device made up of a layer of an induction magnetic transducer for writing and a magnetoresistive (MR) element for reading.
In general, such thin film magnetic heads are formed through cutting a wafer in one direction on which sections to be sliders each including a thin film magnetic head element are arranged in a plurality of rows. A bar-like magnetic head material (called `bar` in the following description) on which the sections to be sliders are arranged in a row is thereby formed. Processing such as lapping is performed on the medium facing surface of the bar. The bar is then cut into the sliders.
In general, in order to stabilize the output characteristic of the magnetic head, it is important to maintain the distance between the magnetic pole and the surface of a recording medium at an extremely small specific value. It is therefore required in magnetic head processing that the flatness of the medium facing surface of the magnetic head precisely falls on a specific value so as to stabilize a floating amount and that the throat height and the MR height of the magnetic head fall within a specific range. The MR height is the length (height) between the edge close to the medium facing surface of the MR element and the opposite edge. The throat height is the length (height) of the magnetic pole of an induction magnetic transducer.
There are several methods for lapping the medium facing surface so as to achieve desired values of the throat height and MR height of a magnetic head. A method generally used and achieving high precision is the method that utilizes a processing jig having functions described later and a lapping apparatus having a function of automatically lapping while applying an appropriate load to the jig and deforming a bar bonded to the jig.
A processing jig used in the method comprises a main body fixed to a lapping apparatus, a retainer that is long in one direction for retaining a bar, and a plurality of load application sections, coupled to the retainer, to which a load is applied for deforming the retainer. The retainer takes a shape of a narrow and long beam that is bent with an application of external force. An external force being applied to the load application sections of the jig, the retainer is bent. The bending of the retainer causes bending of the bar held by the retainer.
A method of lapping a bar using the jig will now be described. In the method, the bar is fixed to the retainer of the jig with an adhesive and so on so that the surface of the bar to be lapped faces outside.
Next, the values of the throat height and MR height of each magnetic head on the bar fixed to the jig are determined through an optical or electrical method. The deviation of the determined values from the target values, that is, the amounts of lapping required, are calculated.
Of the sections to be lapped corresponding to the magnetic head elements on the bar, the section that require more amount of lapping than the other section needs to be more lapped. Therefore, the bar is deformed by applying a load to the load application section so that the surface to be lapped of the section is made convex. On the other hand, the section that require less amount of lapping than the other section needs to be less lapped. Therefore, the bar is deformed by applying a load to the load applied section so that the surface to be lapped of the section is made concave. The bar is lapped by pressing the medium facing surface of the bar against a rotating lapping plate while the bar is deformed.
A series of operation is automatically repeated, including determining the throat height and the MR height of each magnetic head element, calculating the deviation of the determined values from the target values, that is, the amounts of lapping required, and lapping the bar while deforming the bar in accordance with the amounts of lapping required. Variations in the throat heights and the MR heights of the magnetic head elements are thereby modified. Finally, the throat heights and the MR heights of the magnetic head elements fall within a specific range.
A lapping apparatus for performing lapping of a bar as described above is disclosed in U.S. Pat. No. 5,620,356. A jig for lapping magnetic heads is disclosed in U.S. Pat. No. 5,607,340. A lapping control apparatus is disclosed in Japanese Patent Application Laid-open No. Heisei 2-95572 (1990) for controlling a throat height through observing a resistance of an MR element.
In a lapping method using a jig having three section to which a load is applied for bending a retainer, as shown in U.S. Pat. No. 5,607,340 mentioned above, a lapping amount required is calculated based on the determined values of the throat height and the MR height. In accordance with the amount, a load for pushing or pulling is applied to the load application section in a direction orthogonal to the length of the retainer so as to deform the retainer. The bar is lapped in this state so that the throat heights and the MR heights of the magnetic head elements fall within a permissible range.
Although highly precise throat heights and MR heights are more and more required, it is difficult for the lapping method described above to obtain the throat heights and MR heights within the permissible range throughout the length of the bar when the bar of about 50 mm in length, for example, is lapped.
The reasons will now be described. In the jig, a load for deforming the retainer is applied to the three load application points of the retainer in a direction orthogonal to the length of the retainer. The only shape of the retainer obtained through bending approximates to a curve of the fourth order. Consequently, modifiable distribution patterns of throat heights and MR heights are limited to the patterns that approximate to curves of a low order, that is, the fourth order or below. In contrast, although the values of throat heights and MR heights of most magnetic head elements on a bar actually lapped fall within the permissible range if seen in broad perspective, the distribution of the values of throat heights and MR heights of the magnetic head elements on the bar has a more complex pattern that may approximate to a curve of a high order such as a sixth order or above if seen in narrow perspective. As a result, correction of the throat heights and MR heights is not sufficiently performed on the sections that do not meet the distribution pattern of the throat heights and MR heights that may approximate to a curve of a high order as described above. The deviation of the determined values from the target values is not reduced, either. Therefore, some fall off the permissible range of the throat heights and MR heights.
FIG. 25 shows an example of the distribution of final MR heights `MR-h` on a bar when the bar of about 50 mm in length, for example, is lapped with a jig of related art while automatically controlling the throat heights and MR heights. The solid line indicates a regression curve of the sixth order of the distribution of MR heights `MR-h`. The broken line indicates a regression curve of the fourth order of the distribution of MR heights `MR-h`. In the example shown, the distribution of final MR heights `MR-h` on the bar approximates to the regression curve of the sixth order.
Most distribution patterns of MR heights on a bar before lapping regress to curves of the sixth order or above. However, the related-art jigs are capable of correcting distribution patterns of MR heights that approximate to curves of the fourth order or below only. Therefore, as shown in FIG. 25, high-order components remain uncorrected in the distribution pattern of MR heights on the bar after lapping. The same applies to the throat height, too.
If a jig with a fewer (that is, one or two) points to which a load for bending is applied is used, distribution patterns of MR heights that approximate to curves of the still lower order are only correctable. As a result, with such a jig, more throat heights and MR heights fall outside the permissible range.
Several methods have been developed and improved for enhancing the straightness of a distribution pattern of throat heights and MR heights without forcedly deforming a jig. However, while the demand for higher-precision throat height and MR height specifications (a permissible range of .+-.0.01 .mu.m, for example) is growing, it is extremely difficult to maintain the straightness of distribution pattern of throat heights and MR heights throughout the bar with such a high degree of accuracy. It is practically difficult as well to achieve accuracy of the flatness of the lapping surface of a lapping plate and the consistency of a lapping rate throughout the surface. Therefore, the method of controlling throat heights and MR heights without forcedly deforming a jig has limitations in terms of accuracy.
On the other hand, a method of reducing the length of a bar may be used for reducing variations in throat heights and MR heights on a bar. However, the number of magnetic heads processed at a time is reduced in the method. It is therefore required to increase the number of lapping apparatuses. Productivity is thereby reduced.
Alternatively, the number of points of the retainer of the jig to which a bending load is applied may be increased and the number of loading mechanisms of the lapping apparatus may be increased in accordance with high-order components of the distribution pattern of throat heights and MR heights. However, since the loading mechanisms of the lapping apparatus are increased in size and complicated, it is difficult to ensure the reliability of operation of the apparatus. The system costs are increased as well.